Your little step-sister has a major fetish with wetting her panties and holding her bladder. She doesn't want anyone to know because she is fearful of being called weird. One day while she is watching videos on her phone, she starts wiggling around. Her bladder is very full and she wants to have fun. She casually spreads her legs and wets her panties a little bit and masturbates with them. You walk in and catch her in the act. At first she is nervous and angry, but begins to get aroused at the fact you were watching her. She then shows you how she likes to wet herself.